Field of the Invention
The present invention relates to a quantization method and an image processor, and in particular relates to a quantization technology that converts continuous tone images to binary or multivalued images.
Description of the Related Art
An inkjet printer that performs printing on a recording medium such as a paper sheet by a single path system using a print head for which nozzles that eject ink are two-dimensionally arranged is known. In the case that relative vibrations are generated in a paper feed direction between the print head and the paper sheet in such a printer, belt-like irregularities (vibration irregularities) extending along a paper feed vertical direction are generated.
Japanese Patent Application Laid-Open No. 2012-176543 discloses a technology of suppressing irregularities by controlling a halftone pattern in the case that the relative vibrations between the print head and the paper sheet are generated in the paper feed vertical direction (a width direction of paper). By this technology, irregularities generated in the paper feed direction by the relative vibrations in the paper feed vertical direction can be effectively suppressed.
Also, a similar problem occurs also at a joint of head modules of a print head. A print head of the single path system for which a plurality of head modules are alternately shifted in the paper feed direction and arranged in a line in the paper feed vertical direction is known. In such a print head, at a joint area between adjacent head modules, by arranging both head modules so as to overlap in the paper feed direction, nozzles of both head modules are practically alternately arranged along the paper feed vertical direction. Here, when the arrangement in the paper feed direction of the head modules is shifted, a difference is generated in patterns to be printed between the joint area and the other area, and belt-like irregularities (inter-module joint irregularities) extending along the paper feed direction are generated.
Japanese Patent Application Laid-Open No. 2009-018479 and Japanese Patent Application Laid-Open No. 2011-121248 disclose methods of solving problems of graininess deterioration and density fluctuation at a joint between head modules due to a position shift of the head modules or the like by dot distribution and halftone processing.